1. Field of the Invention
The present invention relates to a radio transmission apparatus and radio communication apparatus using polar modulation.
2. Description of the Related Art
FIG. 1 shows a first conventional example of a polar modulation transmitter. A polar modulation transmitter is provided with a polar signal generation circuit 1201, an amplitude control circuit 1202, a phase modulated signal generation circuit 1203 and a non-linear power amplifier 1204. In such a polar modulation transmitter, the polar signal generation circuit 1201 generates a signal corresponding to the amplitude and phase of a transmit modulated signal from an input signal and based on this, the amplitude control circuit 1202 and phase modulated signal generation circuit 1203 generate an amplitude signal and a phase modulated signal respectively. The non-linear power amplifier 1204, which is operating in a non-linear saturation mode, receives the phase modulated signal and carries out amplitude modulation by changing a supply voltage according to the amplitude signal. Thus, operating the non-linear power amplifier 1204 in a non-linear saturation mode can reduce current consumption compared to a case where a linear power amplifier is used and thereby extend a battery life of a battery-operated transmitter (e.g., see Specification of U.S. Pat. No. 6,377,784B2).
FIG. 2 illustrates a second conventional example of a polar modulation transmitter. In addition to a polar signal generation circuit 1301, a timing adjustment circuit 1302, an amplitude control circuit 1305, a phase modulated signal generation circuit 1306 and a power amplifier 1307, this polar modulation transmitter is further provided with an amplitude signal detection circuit 1308, a phase signal detection circuit 1309 and a PA calibration table 1310. By correcting the amplitude control circuit 1305 and phase modulated signal generation circuit 1306 using this calibration table 1310, it is possible to correct amplitude-amplitude distortion (AM-AM distortion) and amplitude-phase distortion (AM-PM distortion) of the power amplifier 1307. Furthermore, the timing adjustment circuit 1302 adjusts timings of an amplitude signal and a phase signal, corrects a delay difference between the amplitude signal and phase signal in their respective paths, and can thereby suppress deterioration of transmission quality due to the delay difference (e.g., see Specification of U.S. Pat. No. 6,366,177B1). For example, according to a W-CDMA standard, transmission quality is expressed by ACLR (Adjacent Channel Leakage Power Ratio) and EVM (Error Vector Magnitude (modulation accuracy)).
FIG. 3 illustrates a third conventional example of a polar modulation transmitter. This polar modulation transmitter includes a modulator section 1410 with delay circuits 1412, 1413 added thereto. It is possible to suppress deterioration of ACLR and EVM due to a delay difference between the amplitude signal and phase signal by adjusting timings of a drain voltage (amplitude) and modulated wave signal (phase) using these delay circuits 1412, 1413 and correcting the delay difference between the amplitude signal and phase signal in their respective paths (e.g., see Japanese Patent Publication No. 6-54877 (FIG. 6)).
FIG. 4 illustrates a fourth conventional example of a polar modulation transmitter. This polar modulation transmitter is provided with phase detection sections 1502, 1503 that detect the phase of an RF output signal, an amplitude detection section 1501 that detects the amplitude envelope of the RF output signal, a synchronization detection section 1512 that detects synchronization between the phase and amplitude of the RF output signal and a synchronization control section 1513 that controls a delay section 1515 based on the detected synchronization. It is possible to suppress deterioration of ACLR and EVM due to the delay difference between the amplitude signal and phase signal by adjusting timings of the amplitude signal and phase signal using these sections and correcting the delay difference between the amplitude signal and phase signal in their respective paths (e.g., see National Publication of International Patent Application No. 2002-530992 (FIG.2)).
However, the first conventional example shown in FIG. 1 is not provided with the timing adjusting section and cannot correct the delay difference between the amplitude signal and phase signal in their respective paths and cannot suppress deterioration of transmission quality due to the delay difference.
Furthermore, the polar modulation transmitters in the second conventional example shown in FIG. 2 and third conventional example shown in FIG. 3 have no synchronization circuit that automatically establishes synchronization between the amplitude signal and phase signal, and therefore there is no other way for adjusting synchronization than manual adjustment. Furthermore, after shipment of a product, it is difficult for a general consumer to adjust synchronization when using the product.
Furthermore, the polar modulation transmitter in the fourth conventional example shown in FIG. 4 is constructed in such a way that an amplitude envelope and phase are detected from an RF output signal of the multiplier or power amplifier. However, detecting synchronization between the amplitude signal and phase signal in such a configuration requires an RF band signal to be demodulated into a baseband by some means, which leads to the use of a circuit such as a low pass filter having a delay whose magnitude cannot be ignored. As a result, a delay variation is produced at the time of detection and the accuracy of detection of the delay difference deteriorates.